In a field of fibers, various kinds of efforts have been made with regard to reduce a fiber diameter and make it to 10 μm or less. That has unique feeling and expensive-looking in apparel usage, and heat-retaining property, heat insulating property and printability are increased with enhanced covering power by increasing fiber density. Further, it is because fiber performances are greatly improved from various points in also industrial and agriculture usage such as to improve greatly flexibility of rope etc., heat-retaining property and also filter features.
Meanwhile, also in fiber industry, biodegradable fibers have been strongly required in also household use, and industrial materials; such as agriculture materials, diaper, packaging materials, etc. for transition to resource recycling type society from a viewpoint of global environment. But, although there is a point of view from raw material cost, it is difficult to make fibers of small fiber diameters as a spinning property and drawing property is bad in also a viewpoint of its manufacturing method and fiber performance (for example, Japanese Patent Laid-Open Hei. 7-305227). In addition, polylactic acid fibers which are typical biodegradable fibers were depended on plasticizer etc. (for example, Japanese Patent Laid-Open 2000-154425) as these are hard and brittle filament and have also a problem from performance side but additives of plasticizer etc. damage strength and heat resistance property and fiber properties are spoiled.
One of essential problematic point that biodegradable fibers have is a request for different biodegradable speed depending on intended end-usage; degradation completion term of rope and sheet for mulching are different in even agriculture usage, and also different from that of a diaper and wiping cloth. It is desired to prepare product groups having various degradation speeds without changing a kind of polymers to fulfill these requests.
Additionally, biodegradable fibers have many usages especially in a non-woven fabric fields and various manufacturing methods are proposed (for example, Japanese Patent Laid-Open 2000-273750 and Japanese Patent Laid-Open 2001-123371). Those are required non-woven fabrics of small filament diameters from a viewpoint of covering power and heat-retaining property of nonwoven fabrics and feeling etc. in a diaper. But, it was difficult to manufacture non-woven fabrics of small filament diameters simply and conveniently and cheaply as performance of spinning and drawing is bad.
In addition, as the broad sense of biodegradable fibers, there are bioerodible absorbable fibers (for example, Japanese Patent Laid-Open Hei. 8-182751) and thin and flexible filament with strength is required for surgical suture threads etc. Additionally, non-woven fabrics consisting of bioerodible absorbable fibers have been used also in various fields such as suture prosthesis, anti-adhesion material, artificial skin and cell culture substratum (for example, Japanese Patent Laid-Open 2000-157622 and Japanese Patent Laid-Open 2004-321484) from medical care side, also in these field, non-woven fabrics consisting of thin filament with strength are required.
On the other hand, the invention relates to drawing technology of filament by infrared rays heating but the technology concerning with these has been performed in many ways conventionally (for example, Japanese Patent Laid Open 2003-166115, pamphlet of International Laid Open No. 00/73556, Akihiro Suzuki, et al. Journal of Applied Polymer Science, Vol. 83, pp. 1711-1716, 2002, Akihiro Suzuki, et al., Preliminary Abstracts of Polymer Science Society, Japan, May 7, 2001, Vol. 50, No. 4, pp. 787, Akihiro Suzuki, et al., Journal of Applied Polymer Science, Vol. 88, pp. 3279-3283, 2003, Akihiro Suzuki, et al., Journal of Applied Polymer Science, Vol. 90, pp. 1955-1958, 2003). The invention, further improving these technologies, is made effectively applicable to biodegradable filament. In addition, a zone drawing method and a zone heat treatment method shown in the literature (Journal of Applied Polymer Science, Vol. 90, pp. 1955-1958, 2003) are beneficial means to conduct also re-drawing or heat treatment of the drawn biodegradable filament of the invention.
Accordingly, the invention solves problematic points of biodegradable filament by further developing the conventional technology of above-mentioned inventor, and the object in the invention resides in to obtain highly drawn and oriented biodegradable micro-filament easily by spinning thick biodegradable filament at stable spinning condition and drawing them to high ratio with simple and convenient means. And the other object resides in to obtain filament used for surgical suture threads etc. which are flexible and have strength by making filament consisting of bioerodible absorbable polymer to be super-micro. Additionally, the other object resides in to be product groups with different biodegradable speed by various product (threads, rope, fabrics, non-woven fabrics and so on) groups different in filament diameters by this simple and convenient drawing means. In addition, the other object resides in to be able to manufacture long fiber non-woven fabrics consisting of biodegradable micro-filament having high degree of molecular orientation. Further, the other object resides in to offer non-woven fabrics consisting of bioerodible absorbable filament, which are used for suture prosthesis, anti-adhesive material, artificial skin, cell culture substratum, etc.